Techniques to enhance diversity for a wireless system

ABSTRACT

A system, apparatus, method and article to manage diversity for a wireless multicarrier communication system are described. An apparatus may include a diversity agent to couple to a transmitter, the diversity agent to convert a determined number of input bits into symbols, interleave the symbols across multiple spatial streams, and map the symbols to tones for each spatial stream. Other embodiments are described and claimed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/095,207, filed on Mar. 30, 2005 now U.S. Pat. No. 7,539,463, entitled“Techniques to Enhance Diversity for a Wireless System” (incorporatedherein by reference in its entirety).

BACKGROUND

Some wireless systems may use multiple antennas, such as amultiple-input, multiple-output (MIMO) system. MIMO systems may usemultiple antennas at both the transmitter and receiver. MIMO systems maytransmit multiple data streams over the multiple antennas to providespatial diversity to the overall communication signal. Spatial diversitymay improve performance of a wireless system, such as providing greaterrange or throughput for the system.

Some wireless system may also use multiple carriers. A multicarriersystem is typically characterized by a frequency band associated with acommunication channel that is divided into a number of smallersub-bands, sometimes referred to as subcarriers. Examples ofmulticarrier systems may include Orthogonal Frequency DivisionMultiplexing (OFDM) systems and Discrete Multi-tone (DMT) systems. Amulticarrier system may communicate information by dividing theinformational content into symbols, and then transmitting the symbols inparallel using a number of subcarriers. Interleaving symbols acrosssubcarriers may provide a form of frequency diversity, which may alsoimprove performance of the system.

The use of spatial diversity or frequency diversity may improve certainaspects of a wireless system. There are limitations, however, to theamount of spatial diversity or frequency diversity available to anygiven system. Consequently, techniques to improve spatial diversityand/or frequency diversity may increase performance of a wirelesssystem.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of a system.

FIG. 2 illustrates one embodiment of a component.

FIG. 3 illustrates one embodiment of a diversity architecture.

FIG. 4 illustrates one embodiment of a logic flow.

FIG. 5A illustrates one embodiment of an example diversity agent.

FIG. 5B illustrates one embodiment of an example diversity agent.

FIG. 6 illustrates one embodiment of a graphical representation.

DETAILED DESCRIPTION

FIG. 1 illustrates one embodiment of a system. FIG. 1 may illustrate ablock diagram of a system 100. System 100 may comprise, for example, acommunication system having multiple nodes. A node may comprise anyphysical or logical entity having a unique address in system 100.Examples of a node may include any network devices, such as a computer,server, workstation, laptop, ultra-laptop, handheld computer, telephone,cellular telephone, personal digital assistant (PDA), router, switch,bridge, hub, gateway, wireless access point, and so forth. The uniqueaddress may comprise, for example, a network address such as an InternetProtocol (IP) address, a device address such as a Media Access Control(MAC) address, and so forth. The embodiments are not limited in thiscontext.

The nodes of system 100 may be arranged to communicate different typesof information, such as media information and control information. Mediainformation may generally refer to any data representing content meantfor a user, such as voice information, video information, audioinformation, text information, numerical information, alphanumericsymbols, graphics, images, and so forth. Control information maygenerally refer to any data representing commands, instructions orcontrol words meant for an automated system. For example, controlinformation may be used to route media information through a system, orinstruct a node to process the media information in a predeterminedmanner.

The nodes of system 100 may communicate media and control information inaccordance with one or more protocols. A protocol may comprise a set ofpredefined rules or instructions to control how the nodes communicateinformation between each other. The protocol may be defined by one ormore protocol standards as promulgated by a standards organization, suchas the Internet Engineering Task Force (IETF), InternationalTelecommunications Union (ITU), the Institute of Electrical andElectronics Engineers (IEEE), and so forth. For example, system 100 mayoperate in accordance with various wireless local area network (WLAN)protocols, such as one or more of the IEEE 802.11 series of protocols.In another example, system 100 may operate in accordance with variouswireless metropolitan area network (WMAN) mobile broadband wirelessaccess (MBWA) protocols, such as a protocol from one or more of the IEEE802.16 or 802.20 series of protocols. The embodiments are not limited inthis context.

Referring again to FIG. 1, system 100 may comprise a wirelesscommunication system. In one embodiment, system 100 may include one ormore wireless communication devices, such as nodes 110, 120, 150. Nodes110, 120, 150 may be arranged to communicate information signals overwireless shared media 160 using one or more wirelesstransmitters/receivers (“transceivers”). Information signals may includeany type of signal encoded with media and/or control information.Although FIG. 1 is shown with a limited number of nodes in a certaintopology, it may be appreciated that system 100 may include more or lessnodes in any type of topology as desired for a given implementation. Theembodiments are not limited in this context.

In one embodiment, system 100 may include nodes 110, 120. Nodes 110, 120may comprise fixed devices having wireless capabilities. A fixed devicemay comprise a generalized equipment set to provide connectivity,management, and control of another device, such as mobile devices.Examples for nodes 1110, 120 may include a wireless access point (AP),base station or node B, router, switch, hub, gateway, and so forth. Inone embodiment, for example, nodes 1110, 120 may comprise base stationsfor a WMAN system. Although some embodiments may be described with nodes1110, 120 implemented as base stations by way of example, it may beappreciated that other embodiments may be implemented using otherwireless devices as well.

In one embodiment, base stations 110, 120 may also provide access to anetwork 170 via wired communications media. Network 170 may representany of a broad range of communication networks including, for example aplain-old telephone system (POTS) communication network, a personal areanetwork (PAN), a local area network (LAN), metropolitan area network(MAN), wide-area network (WAN), global area network (e.g., theInternet), cellular network, and the like. The embodiments are notlimited in this context.

In one embodiment, system 100 may include node 150. Node 150 maycomprise, for example, a mobile device or a fixed device having wirelesscapabilities. A mobile device may comprise a generalized equipment setto provide connectivity to other wireless devices, such as other mobiledevices or fixed devices. Examples for node 150 may include a computer,server, workstation, notebook computer, handheld computer, telephone,cellular telephone, PDA, combination cellular telephone and PDA, one-waypagers, two-way pagers, and so forth. In one embodiment, for example,node 150 may comprise a mobile device, such as a mobile subscriberstation (MSS) for a WMAN. Although some embodiments may be describedwith MSS 150 implemented as a wireless device for a MSS by way ofexample, it may be appreciated that other embodiments may be implementedusing other wireless devices as well. For example, node 150 may also beimplemented as a fixed device such as a computer arranged with awireless transceiver, a mobile station (STA) for a WLAN, and so forth.The embodiments are not limited in this context.

Nodes 110, 120, 150 may have one or more wireless transceivers andwireless antennas. In one embodiment, for example, nodes 110, 120, 150may each have multiple transceivers and multiple antennas. The use ofmultiple antennas may be used to provide a spatial division multipleaccess (SDMA) system or a MIMO system in accordance with one or more ofthe IEEE 802.16 series of standards, such as one or more of the IEEE802.16e proposed standards, for example. The embodiments are not limitedin this context.

In general operation, the nodes of system 100 may operate in multipleoperating modes. For example, nodes 110, 120, 150 may operate in variousoperating modes, such as a single-input-single-output (SISO) mode, amultiple-input-single-output (MISO) mode, a single-input-multiple-output(SIMO) mode, and/or in a MIMO mode. In a SISO operating mode, a singletransmitter and a single receiver may be used to communicate informationsignals over a wireless shared medium 160. In a MISO operating mode, twoor more transmitters may transmit information signals over wirelessshared media 160, and information signals may be received from wirelessshared media 160 by a single receiver of a MIMO system. In a SIMOoperating mode, one transmitter and two or more receivers may be used tocommunicate information signals over wireless shared media 160. In aMIMO operating mode, two or more transmitters and two or more receiversmay be used to communicate information signals over wireless sharedmedia 160. When in a MIMO operating mode, some embodiments may bearranged to operate in a spatial multiplexing mode to further enhanceperformance of system 100.

In one embodiment, one or more nodes of system 100 may use an advancedOFDM processing technique for a MIMO transceiver that utilizes more thanone transmit/receive chain at each end of the wireless link. Thecombination of MIMO and OFDM (MIMO-OFDM) in system 100 may beparticularly desirable for high-throughput WLAN and WMAN applications,for example. The embodiments are not limited in this context.

In one embodiment, the MIMO-OFDM system may use one or more transmitdiversity techniques to provide a near-optimal method for mappinguncoded information received from a host device, or an application/agentexecuting thereon, to multiple antennas and OFDM tones. The uncodedinformation may include, for example, various types of symbols, such asquadrature amplitude modulation (QAM) symbols. The embodiments are notlimited in this context.

While the transmit diversity architecture of some embodiments mayprovide full-order diversity, the transmit diversity architecture mayonly provide a limited code rate per OFDM slot. Consequently, thetransmit diversity architecture may be extended to provide a higher coderate by means of space-frequency interleaving. As developed more fullybelow, space-frequency interleaving provides a near-optimal techniquefor mapping coded information onto multiple antennas and OFDM tones.Examples of coded information may include any type of informationprocessed by an encoding technique, such as forward error correcting(FEC) encoding, convolutional encoding, Reed Solomon encoding, LDPCencoding, trellis encoding, turbo encoding, Bose-Chaudhuri-Hocquenghem(BCH) encoding, and so forth. The embodiments are not limited in thiscontext.

Some embodiments may implement enhanced transmit diversity andspace-frequency techniques to improve performance of a MIMO-OFDM system,such as system 100. In one embodiment, for example, nodes 110, 120, 150may each include a component 108. Component 108 may be arranged toimplement one or more transmit diversity and/or space-frequencytechniques for nodes 110, 120, 150. Component 108 may comprise, amongother elements, a diversity agent. In one embodiment, the diversityagent may perform various combinations of symbol level spatialinterleaving and/or block concatenation. The embodiments are not limitedin this context.

In one embodiment, for example, the diversity agent may perform symbollevel spatial interleaving. The diversity agent may convert a determinednumber of input bits into symbols, interleave the symbols acrossmultiple spatial streams, and map the symbols to tones for each spatialstream. The embodiments are not limited in this context.

In one embodiment, for example, the diversity agent may perform symbollevel spatial interleaving with block concatenation. For example, thediversity agent may group the determined number of input bits into asingle block (e.g., FEC block), and convert the block to symbols (e.g.,QAM symbols). Block concatenation may allow larger blocks relative toother implementations. The embodiments are not limited in this context.

In one embodiment, for example, the diversity agent may perform symbollevel spatial interleaving without block concatenation. For example, thediversity agent may segment the determined number of input bits intomultiple blocks (e.g., FEC blocks), and convert each block to symbols(e.g., QAM symbols). The use of multiple blocks may be implemented withless complexity at the cost of reduced efficiency relative to using asingle block as in other implementations. The embodiments are notlimited in this context.

In some embodiments, the diversity agent may be further arranged toperform a cyclic shift of each spatial stream prior to mapping thesymbols to each spatial stream. This may ensure that adjacent coded bitsare not mapped to the same tone on different antennas, therebypotentially improving performance and providing greater spatialdiversity. These and other embodiments of component 108 may be describedin more detail with reference to FIG. 2.

FIG. 2 illustrates one embodiment of a component. FIG. 2 may illustratea block diagram for component 108 of system 100. Component 108 may beimplemented as part of nodes 110, 120 or 150 as described with referenceto FIG. 1. As shown in FIG. 2, component 108 may comprise multipleelements, such as processor 210, switch (SW) 220, a transceiver array230, and a memory 290. Some elements may be implemented using, forexample, one or more circuits, components, registers, processors,software subroutines, or any combination thereof. Although FIG. 2 showsa limited number of elements, it can be appreciated that more or lesselements may be used in component 108 as desired for a givenimplementation. The embodiments are not limited in this context.

In one embodiment, component 108 may include a transceiver array 230.Transceiver array 230 may be implemented as, for example, a MIMO system.Transceiver array 230 may include two transmitters 240 a and 240 b, andtwo receivers 250 a and 250 b. Although transceiver array 230 is shownwith a limited number of transmitters and receivers for purposes ofclarity, it may be appreciated that transceiver array 230 may includeany desired number of transmitters and receivers. The embodiments arenot limited in this context.

In one embodiment, transmitters 240 a-b and receivers 250 a-b oftransceiver array 230 may be implemented as OFDM transmitters andreceivers. Transmitters 240 a-b and receivers 250 a-b may communicatedata frames with other wireless devices. For example, when implementedas part of base stations 110, 120, transmitters 240 a-b and receivers250 a-b may communicate data frames with MSS 150. When implemented aspart of MSS 150, transmitters 240 a-b and receivers 250 a-b maycommunicate data frames with base stations 110, 120. The data frames maybe modulated in accordance with a number of modulation schemes, toinclude Binary Phase Shift Keying (BPSK), Quadrature Phase-Shift Keying(QPSK), M-ary PSK (MPSK), M-ary QAM (MQAM), QAM, 16-QAM, 64-QAM,128-QAM, 356-QAM, and so forth, depending on a desired coding rate. Theembodiments are not limited in this context.

In one embodiment, transmitter 240 a and receiver 250 a may be operablycoupled to an antenna 260, and transmitter 240 b and receiver 250 b maybe operably coupled to antenna 270. Examples for antennas 260, 270 mayinclude an internal antenna, an omni-directional antenna, a monopoleantenna, a dipole antenna, an end fed antenna, a circularly polarizedantenna, a micro-strip antenna, a diversity antenna, a dual antenna, anantenna array, a helical antenna, and so forth. The embodiments are notlimited in this context.

In one embodiment, transceiver array 230 may comprise any of a varietyof multicarrier wireless communication transceivers known in the art. Inthis regard, a transmitting element of transmitters 240 a-b may receiveinformation from a host device, process the received information togenerate an OFDM transmit signal, and then transmit that OFDM signalover a link (e.g., forward link) to a remote device via one or moreantennas. A receiving element of receivers 250 a-b may receive multipleinstances of the forward link via one or more antennas 260, 270, andselectively process the received signals to extract a representation ofthe originally encoded information. A diversity agent may enabletransceiver array 230 to implement certain MIMO-OFDM operations, asdescribed further below. According to one embodiment, each of thetransmitters 240 a-b and receivers 250 a-b may include one or moreprocessing chains. The embodiments are not limited in this context.

In one embodiment, component 108 may include a processor 210. Processor210 may be implemented as a general purpose processor. For example,processor 210 may comprise a general purpose processor made by Intel®Corporation, Santa Clara, Calif. Processor 210 may also comprise adedicated processor, such as a controller, microcontroller, embeddedprocessor, a digital signal processor (DSP), a network processor, aninput/output (I/O) processor, a media processor, and so forth. Theembodiments are not limited in this context.

In one embodiment, component 108 may include a memory 290. Memory 290may comprise any machine-readable or computer-readable media capable ofstoring data, including both volatile and non-volatile memory. Forexample, the memory may comprise read-only memory (ROM), random-accessmemory (RAM), dynamic RAM (DRAM), Double-Data-Rate DRAM (DDRAM),synchronous DRAM (SDRAM), static RAM (SRAM), programmable ROM (PROM),erasable programmable ROM (EPROM), electrically erasable programmableROM (EEPROM), flash memory, polymer memory such as ferroelectric polymermemory, ovonic memory, phase change or ferroelectric memory,silicon-oxide-nitride-oxide-silicon (SONOS) memory, magnetic or opticalcards, or any other type of media suitable for storing information. Theembodiments are not limited in this context.

In one embodiment, the nodes of system 100 may operate in accordancewith one or more of the IEEE 802.11, 802.16 or 802.20 series ofspecifications. A wireless device operating in accordance with suchspecifications typically requires the implementation of at least twolayers. The first layer is the 802.xx MAC layer. In general, the MAClayer manages and maintains communications between the wireless devicesby coordinating access to a shared radio channel and utilizing protocolsto enhance communications over wireless shared media 160. The secondlayer is the 802.xx physical (PHY) layer. The PHY layer may perform theoperations of carrier sensing, transmission, and receiving of 802.xxframes. The PHY layer is typically implemented using dedicated hardware.The MAC layer, however, is typically implemented using a combination ofdedicated hardware and dedicated software.

In one embodiment, for example, processor 210 may be arranged to performvarious baseband and MAC layer operations. For example, processor 210may be implemented as a media access control (MAC) processor. Inaddition to the typical baseband and MAC layer operations, MAC 210 mayimplement at least a subset of the features of a diversity agent inaccordance with one or more MIMO-OFDM systems, and/or may providecontrol over a diversity agent implemented within associated transceiverarray 230. The embodiments are not limited in this context.

In some embodiments, component 108 may be used to implement a diversityagent. The diversity agent may be arranged to manage one or morediversity elements within the multicarrier wireless channel. On thetransmit side of a communication channel, the diversity agent mayreceive information from a host device, application, agent, and soforth. The diversity agent may selectively map the received informationto multiple antennas and/or OFDM tones to generate a MIMO-OFDM transmitsignal. In support of the receive side of the communication channel, thediversity agent may selectively demap the information received via aMIMO-OFDM wireless channel 106 from multiple antennas and OFDM tones.While not specifically denoted in FIG. 2, the diversity agent may beimplemented by one or more elements of component 108, such as MAC 210,memory 290, and/or transceiver array 230. The embodiments, however, arenot limited in this context.

According to one example embodiment, the diversity agent may selectivelyprocess the received information to implement full-order transmitdiversity. As developed below, the diversity agent may map uncodedinformation (e.g., QAM symbols) received from the host devices orapplications executed thereon, onto multiple antennas and OFDM tones toeffect spatial diversity in the transmit link of channel 106. Theembodiments are not limited in this context.

According to one embodiment, the diversity agent may selectively processthe received information to introduce space-frequency interleavingtechniques to interleave the information onto multiple antennas and OFDMtones. The diversity agent may selectively map coded information (e.g.,bits, bytes, blocks, symbols, frames, packets) received from the hostdevice or applications executing thereon, onto multiple antennas andOFDM tones by performing one or more of antenna multiplexing, 802.xxinterleaving, QAM mapping, and cyclic tone shifting. The embodiments arenot limited in this context.

According to one embodiment, the diversity agent may also selectivelyimplement innovative techniques for decoding information from a receivedOFDM channel. In this regard, the diversity agent may demap and/ordeinterleave information received from wireless shared media 160generated in accordance with one or both of the encoding techniquespreviously described. According to one embodiment, receive diversityagent receives information as decoded modulation information (e.g.,bits) and generates de-mapped and/or de-interleaved information,respectively. The embodiments are not limited in this context.

FIG. 3 illustrates one embodiment of a diversity architecture. FIG. 3may illustrate a block diagram for diversity architecture 390 ofcomponent 108. Diversity architecture 390 may be implemented using oneor more elements of component 108, such as MAC 210, transceiver array230, and/or memory 290 as described with reference to FIG. 2. As shownin FIG. 3, diversity architecture 390 may comprise multiple elements.Some elements may be implemented using, for example, one or morecircuits, components, registers, processors, software subroutines, orany combination thereof. Although FIG. 3 shows a limited number ofelements, it can be appreciated that more or less elements may be usedin diversity architecture 390 as desired for a given implementation. Theembodiments are not limited in this context.

FIG. 3 may provide an example of a transmitter architecture and areceiver architecture according to one example embodiment. To illustratethese architectures within the context of a communication channelbetween two devices, a transmitter from one node (e.g., base station110) and a receiver from another node (e.g., MSS 150) associated with acommunication link are depicted. It may be appreciated that atransceiver in either node (110, 150) may comprise a transmitterarchitecture and a receiver architecture as detailed in FIG. 3, althoughthe embodiments are not limited in this regard. It should also beappreciated that transmitter and receiver architectures of greater orlesser complexity that nonetheless implement the innovative transmitdiversity and/or space-frequency interleaving techniques as describedherein fall within the intended scope of the embodiments.

In one embodiment, diversity architecture 390 may include a transmitterarchitecture 300. Transmitter architecture 300 may comprise one or moreof a serial to parallel (S/P) transform 310, a transmit diversity agent312, one or more inverse discrete Fourier transform (IDFT) elements 314,and a cyclic prefix insertion (CPI) element 316. CPI element 316 may becoupled with one or more antennas 320A . . . M through one or moreassociated radio frequency (RF) elements 318. According to oneembodiment, for example, transmitter architecture 300 may be implementedwithin transceiver array 230. Although depicted as a number of separateoperational elements, it may be appreciated that one or more elements oftransmitter architecture 300 may be combined into a multi-operationalelement, and conversely operational elements may be split into multipleoperational elements without deviating from the intended embodiments.

In one embodiment, transmitter architecture 300 may include S/Ptransform 310. S/P transform 310 may receive information (e.g., bits,bytes, frames, symbols, etc.) from a host device (or, an applicationexecuting thereon, e.g., email, audio, video, etc.) for processing andsubsequent transmission via wireless shared media 160. According to oneembodiment, the received information is in the form of QAM symbols,wherein each symbol represents two bits, b_(i) and b_(j), for example.According to one embodiment, S/P transform 310 takes the information andgenerates a number of parallel substreams of the information, which arepassed to one or more instances of diversity agent 312. Althoughdepicted as a separate operational element, S/P transform 310 may alsobe included within diversity agent 312, or some other elements oftransmitter 300.

According to one embodiment, diversity agent 312 may be arranged toselectively introduce an element of transmit diversity into theinformation streams received from S/P transform 310. In particular,according to one example embodiment, the informational information isselectively mapped to one or more antennas and OFDM tones. According toone example implementation, if information received from the host deviceat diversity agent 312 is not in the form of QAM symbols, diversityagent may perform pre-coding to map the received information to QAMsymbols, although the embodiments are not limited in this regard. Infact, diversity agent may be arranged to introduce transmit diversity toany linear combination of input symbols.

In one embodiment, diversity agent 312 takes the input (e.g., QAMsymbols) and repetitively disperses them (e.g., bits, symbols, etc.)across Mt transmit antennas, and a number (N) of OFDM tones for each ofa plurality of Rayleigh fading channel taps (L), although theembodiments are not limited in this regard. By selectively dispersingthe information in this manner, full order diversity may be achieved, asrepresented by Mt Mr L, where Mr is the number of receive antennas, forexample.

In one embodiment, diversity agent 312 may also include resources toimplement one or more space-frequency interleaving techniques. In thisregard, diversity agent 312 may include one or more operationalelements, such as a block generating element, a randomizing element, anencoding element, a bit interleaving element, an antenna multiplexingelement, a tone interleaving element, a QAM interleaving element, a QAMmapping element and a cyclic tone shifting element, although theembodiments are not limited in this regard. According to one embodiment,diversity agent 312 may treat adjacent coded bits as one symbol, andspreads this information across space and frequency using a transmitdiversity repetition scheme. According to one embodiment, theinformation received from S/P transform 310 is first interleaved acrossat least a subset of transmit antennas Mt, and then across a number ofOFDM tones for each of a plurality of the Rayleigh fading channel taps(L), although the embodiments are not limited in this regard. Theoperational elements may not necessarily need to be applied in the orderdescribed above. Moreover, the amount of cyclic tone shift may bemodified to any value between zero (0) and the number data tones (Nds),and there may be a cyclic shift across antennas instead of, or inaddition to, the shift across tones.

In one embodiment, information from the transmit diversity agent 312 ispassed to one or more inverse discrete Fourier transform (IDFT) elements314. According to one embodiment, IDFT elements 314 may comprise inversefast Fourier transform (IFFT) elements, although the embodiments are notlimited in this regard. According to one embodiment, the number of IDFTelements 314 may be commensurate with the number of transmit antennas,e.g., transmit RF chains. In this regard, IDFT elements 314 may receivea plurality (Z) of encoded substreams from diversity agent 312, andconvert the information from a frequency domain representation to a timedomain representation of the information, although the embodiments arenot limited in this regard.

In one embodiment, IDFT elements 314 may pass the time domaininformation to CPI elements 316. According to one embodiment, CPI 316may introduce a cyclical prefix, or a guard interval in the signal,before it is passed to an RF front-end 318 for amplification, filteringand subsequent transmission via an associated one or more antennas 320A. . . M.

In one embodiment, diversity architecture 390 may include a receiverarchitecture 350. Receiver architecture 350 may extract informationprocessed by transmitter architecture 300. As shown in FIG. 3, an RFfront-end 354 may receive a plurality of signals impinging on one ormore receive antennas 352A . . . N. In accordance with one exampleembodiment, the number (N) of receive antennas is equal to Mr. Accordingto one embodiment, each receive antenna has a dedicated receive chain,where the number of receive front-end elements 354, cyclic prefixremoval (CPR) elements 356 and FFT elements are commensurate with thenumber (N) of receive antennas (e.g., Mr). The embodiments are notlimited in this context.

In on embodiment, RF front end 354 may pass at least a subset of thereceived signals to CPR elements 356. According to one embodiment, CPR356 may remove any cyclic prefix or guard intervals that may have beenintroduced during transmit processing of the received signals. In oneembodiment, CPR 356 may provide the processed information to one or moreassociated FFT elements 358.

According to one embodiment, FFT elements 358 may transform the receivedsignals from an associated receive chain from the time domain to thefrequency domain, for subsequent demultiplexing and decoding of arepresentation of the information embedded within the receivedtransmission. Thus, a plurality of frequency domain representations ofthe received signals may be presented to receive diversity agent 360.

In one embodiment, receive diversity agent 360 may perform acomplementary function to that performed by transmit diversity agent312. In this regard, receive diversity agent 360 may perform thecomplement to the transmit diversity and/or space frequency interleavingintroduced above. In the case of transmit diversity, for example,receive diversity agent 360 may demap the QAM symbols prior to QAMdemodulation and parallel to serial (P/S) conversion 362 extracting arepresentation (I′) of the information encoded within the receivedsignals. In the case of space-frequency interleaving, for example,receive diversity agent 360 may perform deinterleaving and decoding,before providing the output information to P/S transform 362 whichgenerates the representation (I′) of the information encoded within thereceived signals. According to one embodiment, diversity agent 360 mayimplement a minimum mean square error (MMSE) spatial demapper or maximumlikelihood decoding, although the embodiments are not limited in thisregard.

It may be appreciated that the operational blocks of diversityarchitecture 390 may be implemented in hardware, software, firmware, orany combination thereof. Moreover, although not explicitly denoted, itmay be appreciated that one or more elements (e.g., diversity agents312, 360) may receive control input from MAC 210. According to oneembodiment, diversity agents 312, 360 may implement one or more oftransmit diversity and space-frequency interleaving, and communicatewhich MIMO-OFDM scheme is being used through an exchange of channelstate information. In this regard, diversity agents 312, 360 and thetransmit diversity/space-frequency interleaving techniques associatedtherewith, may be adapted according to observed channel delay spread andtransmit or receive antenna correlation information (e.g., channel stateinformation). The embodiments are not limited in this context.

In an IEEE 802.16e MIMO-OFDM system, multiple transmit antennas can beused in diversity mode to provide greater range or in spatialmultiplexing mode to provide higher throughput. Conventional spatialmultiplexing MIMO modes may perform spatial multiplexing on 1-4 transmitantennas, with no coding across transmit antennas. On each antenna,independent with frequency-only bit-interleaved coded modulation(F-BICM) are transmitted. That is, forward error correcting (FEC) blocksof convolutionally coded input bits are interleaved across frequencytones but not across transmit antennas.

In an IEEE 802.16e MIMO-OFDM system such as system 100, however,diversity architecture 390 may implement space-frequency bit-interleavedcoded modulation (SF-BICM). SF-BICM may interleave coded blocks acrossboth spatial streams and frequency tones. Spatial streams are multipledata streams transmitted over multiple antennas, with or without someform of spatial pre-coding such as beamforming, covariance weighting orsingular value decomposition. Space-frequency interleaving may providespatial diversity in to addition to frequency diversity, especially withMMSE spatial filters per tone.

In addition, diversity architecture 390 may also enhance throughput bycommunicating coded blocks across multiple spatial streams. For example,multiple blocks M of a given size B may be formed for transmissionacross M transmission slots of M spatial streams without attempting toconcatenate the blocks across the subchannels using block concatenation.This may be desirable, for example, since it retains the existingelements of the SISO chain and potentially reduces implementationimpact. In another example, a single block of a given size M×B may beformed for transmission across M transmission slots of M spatial streamsthereby concatenating blocks across the subchannels using blockconcatenation. This may be desirable, for example, since larger blocksmay ensure that the number of sub-carriers used to carry the blocks isnot reduced thereby retaining frequency diversity of the system.

To further improve performance, data from a block may be distributedacross the spatial streams using bit interleaving or symbolinterleaving. For example, blocks formed with or without blockconcatenation may be split into M spatial streams after the QAMmodulation symbols are formed. This reduces the amount of changes neededto the channel encoding block used in the SISO interleaver. In anotherexample, blocks may also be split into M spatial streams at the bitlevel using any number of bit level interleaving techniques.

Operations for the above embodiments may be further described withreference to the following figures and accompanying examples. Some ofthe figures may include a logic flow. Although such figures presentedherein may include a particular logic flow, it can be appreciated thatthe logic flow merely provides an example of how the generalfunctionality described herein can be implemented. Further, the givenlogic flow does not necessarily have to be executed in the orderpresented unless otherwise indicated. In addition, the given logic flowmay be implemented by a hardware element, a software element executed bya processor, or any combination thereof. The embodiments are not limitedin this context.

FIG. 4 illustrates one embodiment of a logic flow. FIG. 4 may illustratea block flow diagram of a logic flow 400. Logic flow 400 may berepresentative of the operations executed by one or more systemsdescribed herein, such as diversity architecture 390 as implemented aspart of nodes 110, 120 or 150, for example. As shown in logic flow 400,a determined number of input bits to symbols may be converted at block402. The symbols may be interleaved across multiple spatial streams atblock 404. The symbols may be mapped to tones for each spatial stream atblock 406. Each spatial stream may then be transmitted over a separateantenna. The embodiments are not limited in this context.

In one embodiment, the input bits may be converted at block 402 bygrouping the input bits into a single block, such as a FEC block, forexample. The block may then be converted to symbols. The embodiments arenot limited in this context.

In one embodiment, the input bit may be converted at block 402 bysegmenting the input bits into multiple blocks. Each block may then beconverted to symbols. The embodiments are not limited in this context.

In one embodiment, a cyclic shift of each spatial stream may beperformed prior to mapping the symbols to each spatial stream. This mayimprove performance of a node and provide greater spatial diversity. Theembodiments are not limited in this context.

FIG. 5A illustrates one embodiment of an example diversity agent. FIG.5A illustrates a block diagram of a diversity agent 500. In oneembodiment, diversity agent 500 may be arranged to perform symbol levelspatial interleaving. Diversity agent 500 may be representative of, forexample, diversity agent 312 on the transmit side as described withreference to FIG. 3. It may be appreciated that the operational elementsof diversity agent 500 may be reversed for implementation by diversityagent 360 on the receive side. The embodiments are not limited in thiscontext.

As shown in FIG. 5A, diversity agent 500 may comprise multiple elements,such as block generator 502, randomizer 504, encoder 506, bitinterleaver 508, modulator 510, S/P transform 512, and mapping elements516-1-r. Some elements may be implemented using, for example, one ormore circuits, components, registers, processors, software subroutines,or any combination thereof. Although FIG. 5A shows a limited number ofelements, it can be appreciated that more or less elements may be usedin diversity agent 500 as desired for a given implementation. Theembodiments are not limited in this context.

In one embodiment, block generator 502 may receive a stream of inputbits 502. Input bits 502 may represent any number of bits. In oneembodiment, for example, the bits may comprise uncoded bits having apredetermined size of M×B bits. Block generator 502 may form the M×Bbits into one or more blocks of bits. In one embodiment, for example,block generator 502 may group the M×B input bits into a single block ofM×B bits in order to perform block concatenation, as described in moredetail below. In one embodiment, for example, block generator 502 maysegment the M×B input bits into multiple blocks M of B bits each. Blockgenerator 502 may output the one or more blocks to randomizer 504.

In one embodiment, randomizer 504 may randomize or reorder the bitswithin each block. Randomizer 504 may output the randomized blocks toencoder 506.

In one embodiment, encoder 506 may perform coding for the bits withineach block using a number of encoding techniques. Examples of codingtechniques may include FEC encoding, convolutional encoding, ReedSolomon encoding, LDPC encoding, trellis encoding, turbo encoding, BCHencoding, and so forth. In one embodiment, for example the incominguncoded bits are grouped into blocks of size MB bits and encoded with aconvolutional code and punctured. Encoder 506 may output the codedblocks to bit interleaver 508.

In one embodiment, bit interleaver 508 may perform bit interleaving ofbits within each block. Bit interleaver 508 may distribute the adjacentcoded bits across tones in order to provide frequency diversity. Ingeneral, adjacent bits in a convolutionally coded sequence should beplaced on tones separated by at least one coherence bandwidth in orderto extract full frequency diversity in a frequency selective channel. Aregular spacing of adjacent bits across tones may be desirable. In oneembodiment, for example, bit interleaver 508 may perform bitinterleaving in accordance with one or more IEEE 802.16e proposedstandards. Bit interleaver 508 may output the interleaved block tomodulator 510.

In one embodiment, modulator 510 may map the bits within each block tosymbols. In one embodiment, for example, modulator 510 may Gray map thebits within each block to QAM symbols. Modulator 510 may output the QAMsymbols to S/P transform 512.

In one embodiment, S/P transform 512 may multiplex the symbols acrossmultiple spatial streams 518-1-s, with each spatial stream correspondingto a different antenna 320A . . . M, for example. For example, the QAMsymbols may be multiplexed to mappers 516-1-r. Mappers 516-1-r may mapeach received QAM symbol to one or more tones in the assignedsubchannels in accordance with, for example, the IEEE 802.16esub-channelization and tone-mapping techniques. In one embodiment, thesame set of tones is occupied on each spatial stream 518-1-s. Spatialstreams 518-1-s may be processed in accordance with the remainingelements of diversity architecture 390 as described with reference toFIG. 3 for transmission to one or more remote devices via antennas 320A. . . M.

In one embodiment, diversity agent 500 may be arranged to perform symbollevel spatial interleaving with block concatenation. For example, blockgenerator 502 may group the M×B input bits into a single block of M×Bbits to perform block concatenation. A single block of a given size M×Bmay be formed for transmission across M transmission slots of M spatialstreams thereby concatenating blocks across the subchannels. Theembodiments are not limited in this context.

In one embodiment, diversity agent 500 may be arranged to perform symbollevel spatial interleaving without block concatenation. For example,block generator 502 may segment the M×B input bits into multiple blocksM of B bits each. Multiple blocks M of a given size B may be formed fortransmission across M transmission slots of M spatial streams withoutattempting to concatenate the blocks across the subchannels. Theembodiments are not limited in this context.

FIG. 5B illustrates one embodiment of an example diversity agent. FIG.5B illustrates a block diagram of diversity agent 500 as described withreference to FIG. 5A. As shown in FIG. 5B, diversity agent 500 may bemodified to include multiple cyclic shifters 514-1-p. Cyclic shifters514-1-p may introduce a cyclic shift of m−1 tones to the symbol sequencemapped to the m^(th) antenna. This ensures that adjacent coded bits arenot mapped to the same tone on different antennas. If adjacent tones aremapped to the same tone on different antennas, an MMSE receiver maycorrelate the noise on all the bits thereby degrading performance.Placing adjacent bits on different tones on different antennasde-correlates noise on adjacent bits, thus potentially improvingperformance and providing greater spatial diversity. As with theprevious embodiments described with reference to FIG. 5A, cyclicshifting operations may be performed in conjunction with symbol levelspatial interleaving implemented with block concatenation or withoutblock concatenation, as desired for a given set of design constraints.The embodiments are not limited in this context.

FIG. 6 illustrates one embodiment of a graphical representation. FIG. 6may be used to illustrate certain performance improvements of someembodiments relative to alternate techniques. As shown by FIG. 6, someembodiments may potentially provide superior performance while reducingcomplexity and impact to existing 802.16 standards, thereby providing adesirable solution for a given set of design constraints.

FIG. 6 illustrates a graph of packet error rate (PER) values versussignal to noise ratio (SNR) values for various embodiments. Performanceof three schemes is shown in FIG. 6, including: (1) a SF-BICM labeled“-h Bit Intlv”, (2) a spatial multiplexing labeled “x-No Intlv”, and (3)a symbol interleaver labeled “-0-Sym Intlv.” The block interleaver takesconsecutive blocks of B bits and multiplexes them to different antennas.Therefore bits on different transmit antennas are independent. On eachantenna, 802.16e interleaving is followed. This technique (e.g., F-BICM)is expected to provide frequency diversity but no spatial diversity. Thesymbol interleaver multiplexes consecutive coded QAM symbols ondifferent antennas. This technique (e.g., SF-BICM) is expected toprovide some frequency diversity and some spatial diversity.

In FIG. 6, the slopes of MIMO+SFI are sharper than those of MIMO+SM,suggesting better diversity. Performance of symbol interleaving lies inbetween SF-BICM and F-BICM. With higher frequency diversity, SF-BICMoutperforms F-BICM by 3 dB at a PER of 10%. SF-BICM provides a highergain for lower data rates, extending the connectivity and cell range.The MMSE receiver induces correlation across antennas because ofcross-talk, and the channel induces correlation across tones because oflimited delay spread. Together these two factors induce correlationamong adjacent tones on all antennas. Using a bit interleaver, bits maybe placed on uncorrelated tones and antennas, thereby potentiallyimproving performance with the MMSE receiver.

As further shown in FIG. 6, there is a limited difference between symboland bit interleaving techniques using 16-QAM. For lower order modulationschemes, it appears that bit interleaving may provide betterperformance. Symbol level spatial interleaving, however, can obtain upto 1.5 dB of gain relative to conventional techniques.

It should be understood that the embodiments may be used in a variety ofapplications. As described above, the circuits and techniques disclosedherein may be used in many apparatuses such as transmitters andreceivers of a radio system. Transmitters and/or receivers intended tobe included within the scope of the embodiments may include, by way ofexample only, WLAN transmitters and/or receivers, MIMOtransmitters-receivers system, two-way radio transmitters and/orreceivers, digital system transmitters and/or receivers, analog systemtransmitters and/or receivers, cellular radiotelephone transmittersand/or receivers, and so forth. The embodiments are not limited in thiscontext.

Types of WLAN transmitters and/or receivers intended to be within thescope of the embodiments may include, although are not limited to,transmitters and/or receivers for transmitting and/or receiving spreadspectrum signals such as, for example, Frequency Hopping Spread Spectrum(FHSS) or Direct Sequence Spread Spectrum (DSSS) OFDM transmittersand/or receivers, and so forth. The embodiments are not limited in thiscontext.

Numerous specific details have been set forth herein to provide athorough understanding of the embodiments. It will be understood bythose skilled in the art, however, that the embodiments may be practicedwithout these specific details. In other instances, well-knownoperations, components and circuits have not been described in detail soas not to obscure the embodiments. It can be appreciated that thespecific structural and functional details disclosed herein may berepresentative and do not necessarily limit the scope of theembodiments.

It is also worthy to note that any reference to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. The appearances of the phrase “in oneembodiment” in various places in the specification are not necessarilyall referring to the same embodiment.

Some embodiments may be implemented using an architecture that may varyin accordance with any number of factors, such as desired computationalrate, power levels, heat tolerances, processing cycle budget, input datarates, output data rates, memory resources, data bus speeds and otherperformance constraints. For example, an embodiment may be implementedusing software executed by a general-purpose or special-purposeprocessor. In another example, an embodiment may be implemented asdedicated hardware, such as a circuit, an application specificintegrated circuit (ASIC), Programmable Logic Device (PLD) or digitalsignal processor (DSP), and so forth. In yet another example, anembodiment may be implemented by any combination of programmedgeneral-purpose computer components and custom hardware components. Theembodiments are not limited in this context.

Some embodiments may be described using the expression “coupled” and“connected” along with their derivatives. It should be understood thatthese terms are not intended as synonyms for each other. For example,some embodiments may be described using the term “connected” to indicatethat two or more elements are in direct physical or electrical contactwith each other. In another example, some embodiments may be describedusing the term “coupled” to indicate that two or more elements are indirect physical or electrical contact. The term “coupled,” however, mayalso mean that two or more elements are not in direct contact with eachother, but yet still co-operate or interact with each other. Theembodiments are not limited in this context.

Some embodiments may be implemented, for example, using amachine-readable medium or article which may store an instruction or aset of instructions that, if executed by a machine, may cause themachine to perform a method and/or operations in accordance with theembodiments. Such a machine may include, for example, any suitableprocessing platform, computing platform, computing device, processingdevice, computing system, processing system, computer, processor, or thelike, and may be implemented using any suitable combination of hardwareand/or software. The machine-readable medium or article may include, forexample, any suitable type of memory unit, such as the examples givenwith reference to FIG. 2. For example, the memory unit may include anymemory device, memory article, memory medium, storage device, storagearticle, storage medium and/or storage unit, memory, removable ornon-removable media, erasable or non-erasable media, writeable orre-writeable media, digital or analog media, hard disk, floppy disk,Compact Disk Read Only Memory (CD-ROM), Compact Disk Recordable (CD-R),Compact Disk Rewriteable (CD-RW), optical disk, magnetic media, varioustypes of Digital Versatile Disk (DVD), a tape, a cassette, or the like.The instructions may include any suitable type of code, such as sourcecode, compiled code, interpreted code, executable code, static code,dynamic code, and the like. The instructions may be implemented usingany suitable high-level, low-level, object-oriented, visual, compiledand/or interpreted programming language, such as C, C++, Java, BASIC,Perl, Matlab, Pascal, Visual BASIC, assembly language, machine code, andso forth. The embodiments are not limited in this context.

While certain features of the embodiments have been illustrated asdescribed herein, many modifications, substitutions, changes andequivalents will now occur to those skilled in the art. It is thereforeto be understood that the appended claims are intended to cover all suchmodifications and changes as fall within the true spirit of theembodiments.

1. A method, comprising: concatenating multiple groups of bits into asingle block having a block size based at least on a number of multiplespatial streams; encoding the single block; generating symbols from theencoded single block; distributing the symbols across the multiplespatial streams; and performing a cyclic shift of each spatial streamsuch that adjacent bits are mapped to different tones on differentantennas.
 2. The method of claim 1, further comprising transmitting eachspatial stream over a separate antenna.
 3. The method of claim 1,further comprising mapping said symbols to tones for each spatialstream.
 4. The method of claim 3, wherein each of said tones correspondsto an orthogonal frequency division multiplexing (OFDM) subcarrier. 5.The method of claim 1, further comprising converting each spatial streaminto a time domain representation.
 6. The method of claim 5, whereinsaid converting each spatial stream into a time domain representationcomprises performing a fast fourier transform (FFT).
 7. A system,comprising: multiple antennas; a transceiver array to couple to saidmultiple antennas; a diversity agent coupled to said transceiver array,the diversity agent to concatenate multiple groups of bits into a singleblock having a block size based at least on a number of multiple spatialstreams, encode the single block, generate symbols from the encodedsingle block, distribute the symbols across the multiple spatialstreams, and perform a cyclic shift of each spatial stream.
 8. Thesystem of claim 7, wherein the diversity agent is to map said symbols totones for each spatial stream.
 9. The system of claim 8, wherein each ofsaid tones corresponds to an orthogonal frequency division multiplexing(OFDM) subcarrier.
 10. The system of claim 7, wherein the cyclic shiftof each spatial stream comprises mapping adjacent bits to differenttones on different antennas of the multiple antennas.
 11. The system ofclaim 7, said transceiver array to receive each spatial stream from saiddiversity agent, and to convert each spatial stream into a time domainrepresentation before selectively directing the time domain informationto said multiple antennas for transmission to a remote device.
 12. Thesystem of claim 11, wherein said transceiver array is to direct eachspatial stream to a separate antenna.
 13. The system of claim 11,wherein said converting each spatial stream into a time domainrepresentation comprises performing a fast fourier transform (FFT). 14.The system of claim 11, wherein said converting each spatial stream intoa time domain representation comprises performing orthogonal frequencydivision multiplexing (OFDM).
 15. An article comprising acomputer-readable storage medium containing instructions that ifexecuted enable a system to: concatenate multiple groups of bits into asingle block having a block size based at least on a number of multiplespatial streams; encode the single block; generate symbols from theencoded single block; distribute the symbols across the multiple spatialstreams; and perform a cyclic shift of each spatial stream such thatadjacent bits are mapped to different tones on different antennas. 16.The article of claim 15, wherein the computer-readable storage mediumfurther contains instructions that if executed enable the system totransmit each spatial stream over a separate antenna.
 17. The article ofclaim 15, wherein the computer-readable storage medium further containsinstructions that if executed enable the system to map said symbols totones for each spatial stream.
 18. The article of claim 17, wherein eachof said tones corresponds to an orthogonal frequency divisionmultiplexing (OFDM) subcarrier.
 19. The article of claim 15, wherein thecomputer-readable storage medium further contains instructions that ifexecuted enable the system to convert each spatial stream into a timedomain representation.
 20. The article of claim 19, wherein saidconverting each spatial stream into a time domain representationcomprises performing a fast fourier transform (FFT).